1. Field of the Invention
This invention is generally directed to fasteners having opposing and spreadable shank portions that diverge outwardly relative to one another in order to trap a plug of material there between as the fasteners are driven into a base material. More specifically, the invention is directed to such fasteners that are particularly well suited for use to securing roofing felts, insulations and membranes to cementitious and/or composite materials.
2. Brief Description of the Related Art
In the commercial roofing industry, cast in-place roofing decks are formed using gypsum, light weight concrete, Zonolite®, perlite, vermiculite and other cementitious materials. After being poured, such materials are sealed against the weather by covering with felts, plastics and other types of membranes that are secured using various types of fasteners. The fasteners are thereafter covered with asphalt, adhesive or other plastic sealants, often followed by additional layers of membrane, thereby forming a waterproof assembly.
In U.S. Pat. No. 3,710,672 to Hallock an early form of spreadable fastener is disclosed having particular utility for securing roofing felt or roofing papers to poured lightweight materials such as insulating concrete used in the roofing industry. The fastener included a pair of legs or shank segments that spread apart when driven into cementitious material to thereby trap a plug of the poured lightweight material there between. The plug of material serves as an anchor to retain the fastener locked to the roof deck. An improvement on this patent was issued as U.S. Pat. No. 4,032,802, also to Hallock. The improved fastener provided beveled cutting edges along the penetrating tip of the spreadable legs or shank segments for the purpose of permitting the fastener to easily and cleanly penetrate roofing felts, papers, plastics or other membranes without tearing or ripping the membranes which would result in failure of the integrity of the seal provided by the membrane system.
One of the major problems associated with cementitious roofing systems is that the sealing membranes can be damaged under high wind conditions such as encountered during hurricanes and tornadoes. Pressure changes across the surface of the sealing membranes can create uplifting forces that can pull anchoring fasteners from the cementitious material or rip the membranes around the heads of the fasteners used to secure the membranes in place.
In view of the foregoing, there is a need to provide fasteners for poured roof deck systems that provide not only an increased resistance to withdrawal forces but also increase the surface engagement with the sealing membranes to thereby reduce the possibility of membrane tearing about the head of a fastener.